Dr Susan Dimbi
LIKE any other crop farming practices, tobacco production is reliant on the use of various agro-chemicals, namely insecticides, herbicides, fungicides, and suckercides for the management of a multitude of pests and diseases that affect the crop. While effective and essential, it is undeniable that many agro-chemicals potentially have harmful effects on the handler, the environment and to the end user of the tobacco leaf if mishandled.
When not stored, handled and applied properly pesticides can negatively impact the health of humans, animals and the ecosystems. Major risks associated with frequent use of pesticides and fertilisers are soil and water pollution, the emergence of resistant strains of weeds and pests to pesticides, ecological instability and toxicity to the human and other organisms. For example, the indiscriminate and continuous use of agrochemicals will not only contaminate the environment but can result in the inadvertent killing of beneficial insects, which interferes with natural pest control and can lead to pests and pathogens becoming resistant to the chemicals.
As part of the strategy to enable sustainable tobacco production, there is need for growers and other stakeholders to carefully select agro-chemical use patterns that mitigate these risks. This paper outlines practical measures to eliminate or minimise the harmful effects of agrochemicals that growers and handlers of pesticides can take.
Minimise Pesticide Use by Practising IPM
It is not always necessary to apply an agro-chemical, for the management of a disease or pest problem. Growers can successfully reduce agro-chemicals used on the farm, if they implement an Integrated Pest Management (IPM) strategy. An IPM is an ecosystem-based strategy that focuses on long-term prevention of pests or their damage through a combination of techniques that include modification of cultural practices, habitat manipulation, biological control and the use of resistant varieties. Pesticides are then only used after monitoring indicates they are needed, based on established guidelines, and treatments are made with the goal of eliminating only the target organism.
In Zimbabwe, pest prevention strategies that growers have successfully used for decades include implementing recommended crop rotations, early tobacco stalk destruction, early planting and the selection and use of nematode and disease resistant cultivars. Research done at the TRB shows that crops established early, September and October have fewer pest problems than late planted crops. Furthermore, TRB developed tobacco varieties have varying levels of resistances to a wide range of the economically important diseases. Thus, an early planted, nematode resistant variety would require fewer agro-chemicals than a late planted susceptible one.
It is also necessary to ensure the crop is always growing optimally through timely application of the correct amounts of fertilisers, timely weeding and sucker control. This is because a healthy and vigorously growing crop is less prone to attack by pathogens and pests than a weak, stressed crop.
Early disease and pest detection is Key
A regular, systematic scouting and monitoring routine of the crop is important, as it enables early detection of pests or pathogens, before populations have peaked and control has become much more difficult. It also enables growers to correctly identify the problem pest correctly and determine the severity of the problem and level of intervention required. Scouting and monitoring are also crucial steps that enable the grower to make informed decisions about how best to manage the pest or disease problem. For example, when a crop has low levels of infestation, other control measures such as handpicking in the case of budworm or stinkbug may be deployed as it may not be worthwhile to apply a pesticide.
Scouting should ideally commence as soon as plants begin to grow or pests become active and should continue until the crop is harvested or the risk of pest pressure has passed. Common approaches to monitoring for disease infections or pest infestations include inspection of the crop, by walking in an X, Z or a W pattern to cover the whole field while carefully examining individual plants per determined unit area. In seedbeds and greenhouses placing of yellow sticky traps in the crop will enable the detection of insect pests such as adult whiteflies, leaf miner and fungus gnat.
Select for use, only approved agro-chemicals
The Zimbabwean tobacco Industry exports most of the crop each year to manufacturing companies world-wide. To assist growers select appropriate pesticides for use on tobacco and ensure that the exported crop is free of pesticide residues, the Tobacco Research Board operates an Agro-chemical Countenancing Scheme. Thus, the use of agrochemicals on tobacco is restricted to those countenanced by the Tobacco Research Board through the Pesticide Approval Scheme Service (PASS). This scheme, which has been operating since 1964 involves the TRB screening all tobacco agrochemicals for efficacy, timing and method of application and ensuring that pesticide residues on the leaf are within the internationally acceptable levels. The CORESTA Guidance Residue Levels (GRLs) is one of the standards used.
Annually, well over 100 agrochemicals including new active ingredients on tobacco, those from new sources and new formulations are evaluated. Additionally, with the worldwide banning and phasing-out of a number of agrochemicals for use on tobacco the Tobacco Research Board has also increasingly been searching and screening for greener alternatives to replace the proscribed ones.
Growers and consumers of the Zimbabwean tobacco crop can absolutely be certain that as a result of the comprehensive testing programme, agrochemicals approved and recommended for use on tobacco have been increasingly following principles of Good Agricultural practice (GAP).
A PASS-update, listing all products recommended for use, those under tests and those no longer recommended for use is sent out to growers and merchants annually. From time to time agrochemicals deemed unsafe and proscribed for use are dropped from the list and new safer products are added to the list as they become available. Growers can access the list online, on the TRB website and various social media platforms that the TRB uses for advisory.
Occasionally, during screening of new formulations and products from new sources, incidences of crop phytotoxicity have been encountered and the relevant agrochemical company advised to ensure the products are not sold to growers. The fact that there have seldom been massive losses from phytotoxicity over the years can be attributed to this proactive screening and ensuring that only products deemed safe and effective reach the Zimbabwean market. Additionally, the fact that there have rarely been reports of unacceptable residue levels on the Zimbabwean leaf, can possibly be attributed largely to the fact that the Zimbabwean growers have religiously followed the PASS advisory and been responsible in their use of agrochemicals.
Ensure Timely and Proper Application of Agrochemicals
To ensure maximum effectiveness of an agro-chemical and that no unacceptable levels of residues are left on the leaf, applications must be properly timed. All agrochemical for use on tobacco in Zimbabwe have clear instructions on the timing of application on the label. An example of agro-chemicals for which timing is extremely important are copper-based products such as Copper Oxychloride and Cupric hydroxide used for the management of wildfire and angular leaf spot on tobacco. These fungicides must never be used in the field but only applied during the seedbed season to ensure there are no residues in the leaf by harvest time.
Growers should also be aware that the potential for harmful pesticide exposure is greater when handling concentrated pesticides before dilution than when using a diluted solution. It is thus imperative to be especially careful during the mixing and loading process. For example, pesticides should not be added to a spray tank by lifting the pesticide container above one’s head to pour into the tank.
Use appropriate personal protective equipment
To minimise pesticide effects on human health, farmers have to use appropriate personal protective equipment and clothing (PPE/C) in all stages of pesticide handling. The world over, a key strategy to prevent or reduce workers’ pesticide exposures in agriculture is through providing and promoting the use of Personal Protective Equipment and Clothing (PPE/C). The use of appropriate equipment and clothing is necessary as those tasked with applying pesticides to a crop may be exposed to harmful levels during transportation of the agrochemical, preparation of spray solutions and during or after pesticide application. In particular, handlers can be affected by pesticides in different ways that include oral and dermal exposure and or through inhalation. Workers should take all reasonable steps to minimise risk to themselves, by using all devices provided for their protection or the protection of others, carefully. This includes examining the equipment before beginning work and reporting forthwith to their immediate supervisor any situation which they believe could present a risk if it is something which they cannot properly deal with themselves.
In August 2020, the Government of Zimbabwe, gazette Statutory Instrument 197 of 2020 (Collective Bargaining Agreement: Agricultural Industry-Occupational Safety, Health and Environment Code), which provides guidelines for the proper handling and use of agrochemicals in agriculture, amongst other General Hazard Control Guidelines. It is essential for growers to familiarise with and ensure laid out safety procedures are followed.
Ensure training is conducted before commencing sprays
To reduce growers’ exposure to pesticides, it is essential for them to acquire training on both the technical aspects of pesticide application and on safe handling aspects (Fig 4). Safety training is entails that trainees receive instruction in hazard recognition, and available control measures. It also includes training on safe work practices, proper use of personal protective equipment and emergency procedures and preventive actions.
Ensure proper storage and safe disposal of empty pesticide containers
The safe handling of agrochemicals also includes proper storage and the disposal of the empty pesticide containers. This is because even after the contents have been used up, empty pesticide containers still pose considerable risks to the health of people and the environment. As the first port of call, growers must look out for and be guided by the ‘Storage and Disposal’ statement on the product label.
However, the general guidelines are that to ensure safety, pesticide storage facilities must be cited away from the main buildings and must be well ventilated (to prevent inhalation) and have adequate lighting. Maintain adequate aisle space between container rows to allow inspection for leaks, breaks, or other damage. A first aid kit, spill kit (sand and sawdust in metal buckets) and a fire extinguisher should be kept in the storage building.
Growers must never keep empty pesticide containers as there is a danger that they could be reused for storing food or water and any residues in the containers could pose the risk of poisoning to people or animals. Thus, after use, pesticide containers must be emptied and triple rinsed for disposal or recycling. After triple-rinsing, containers meant for disposal must have holes punched in them to prevent re-use. During this operation, the handler must be sure to wear protective clothing such as chemical resistant gloves and eye protection when rinsing pesticide containers.
While making efforts to increase yields and ensure the production of a quality crop, growers must always take into consideration issues to do with human health, environment and the ecosystem. They must therefore consciously select and adopt practices that reduce total reliance on conventional pesticides. In cases where agro-chemicals have to be used it is necessary to comply with all procedures and practices relating to safety in their use.
Agronomists and those who work closely with growers must endeavor to assist growers select less toxic and hazardous chemicals for use. They must also ensure awareness among growers and handlers regarding the risks and hazardous effect of agrochemicals through continuous training exercises.
The Tobacco Research Board will continue to search for, evaluate and avail growers with greener, less toxic agrochemicals and crop management options. This will no doubt ensure that the Zimbabwean crop continue to be grown in a responsible and sustainable manner.
